1. Field of the Invention
The present invention relates to a method of forming a silicon nitride deposited film as a highly functional passivation film, utilizing a high-frequency discharge under low-temperature conditions, particularly to a method of forming a silicon nitride deposited film mainly on a product having an organic film or made using a resin substrate.
2. Related Background Art
In recent years, there is a need for passivation films for organic electroluminescent (EL) devices or products having semiconductor films formed on resin substrates.
With these products, it is essential to form deposited films under temperature conditions of about 100° C. or lower, which has not been required in the formation of gate insulating films or passivation films of the conventional thin film transistors.
Hitherto, silicon nitride films used mainly as insulating films or passivation films have been formed by the plasma CVD that uses a high-frequency plasma of a frequency of 13.56 MHz or a further higher frequency such as VHF and decomposes a mixed gas of silane, ammonia and nitrogen to deposit a film. Further, high-speed film forming method of forming silicon nitride films has been realized in which the plasma exciting frequency has been increased from 13.56 MHz in the HF band to 30 MHz or more in the VHF band. The formation of these silicon nitride films is usually carried out by supplying a large electric power to the plasma while heating the substrate at about 300° C.
However, with organic EL devices or products using semiconductors or resin materials of poor heat resistance, the use of the conventional silicon nitride film forming method that uses a large electric power while heating the substrate to high temperatures has poses a problem of breakage of organic matters or deformation of resin members due to ion bombardment or heat of the plasma.
Further, when silicon nitride films are to be formed by the conventional method without heating the substrate, there have been created problems such as generation of film peeling off, low deposition rates of 1-2 Å/sec or less, and formation of a large amount of silicon polymer powder that necessitates frequent cleaning of the interior of the chamber to decrease the operating rate of the production system and degrades the product quality.
As described so far, with the conventional method, it is difficult to form passivation films for organic films or semiconductors, which are less resistant to ion bombardment or heat of plasma.
Japanese Patent Application Laid-Open No. 9-289210 discloses a method of forming a silicon nitride film. This publication reports that high-speed film formation has been realized by setting the plasma frequency at 30 MHz to 100 MHz, setting the gas pressure of the atmosphere for film formation within the range of 50 Pa to 180 Pa and establishing such a condition as to satisfy the relation of (S/F) <30 when defining the area of a substrate holder as S (cm2) and defining the flow rate of monosilane as F substrate area (cm2) for film deposition to the flow rate (sccm) of monosilane gas to less than 30, that is, to supply a large amount of monosilane relative to the substrate area for film deposition, thereby achieving high-speed film formation in a large area.
U.S. Pat. No. 6,326,304 discloses a method of producing an amorphous silicon-based thin film photoelectric converter using a silane-based gas and a dilution gas containing hydrogen.
According to this patent, the film-forming rate is improved and the utilization efficiency of source gases is increased by forming an amorphous silicon-based thin film under such conditions that the partial pressure of the silane-based gas in the plasma CVD reaction chamber ranges from 1.2 Torr to 5.0 Torr, and the interval between a surface of a substrate mounted on one electrode and a surface of the other electrode ranges from 8 mm to 15.
However, even with the methods disclosed in Japanese Patent Application Laid-Open No. 9-289210 and U.S. Pat. No. 6,326,304, although high speed film formation can be realized, it is difficult to attain formation of a silicon nitride film with good film quality at low temperatures, film formation with less damage to semiconductor films, and prevention of the deformation of resin members, which the present inventors have been seeking.